Hurler syndrome is a genetic disorder that affects young children between 6 months and 2 years old. Their development is stunted so that they are short for their age, and these children have mental retardation and learning disabilities. Children with Hurler syndrome also experience many organ disorders such as heart disease, breathing difficulties, blindness, deafness and joint stiffness. Many of these children do not survive beyond the age of 10.
Hurler syndrome affects approximately 1 in 100,000 people. It is caused by a deficiency of the enzyme alpha-L-iduronidase. This enzyme is responsible for the breakdown of long chains of sugars known as glycosaminoglycans into smaller sugar molecules. When the enzyme alpha-L-iduronidase is defective, glycosaminoglycans build up inside small vesicles within the cells known as lysosomes.
Hurler syndrome belongs to a group of lysosomal storage disorders known as mucopolysaccharidoses. These are all genetic disorders producing defective enzymes, resulting in an accumulation of long chain sugars within lysosomes. The accumulation of the long chain sugars within the lysosomes disturbs cell function and causes disease.
Hurler syndrome is suspected when the child has symptoms associated with the disease, such as delayed growth, mental retardation, heart and joint problems. Physical signs seen on examination of the child, such as the typical facial features of short nose, flat face and large head, also suggest the child has Hurler syndrome. Children with Hurler syndrome usually have an enlarged liver and spleen that can be felt on examination of the abdomen.
The diagnosis of Hurler syndrome is confirmed by a blood test that measures the level of activity of the enzyme alpha-L-iduronidase. Genetic testing, where mutations in the alpha-L-iduronidase gene are detected, can also be done to confirm the diagnosis.
The treatment of Hurler syndrome requires the replacement of the enzyme alpha-L-iduronidase. Aldurazyme is an intravenous medication which is given on a weekly basis. Aldurazyme needs to be taken for the entire lifetime. Side effects of Aldurazyme include discomfort or bruising at the site of injection.
Another treatment for Hurler syndrome is bone marrow transplantation. The bone marrow may come from a relative or a matched unrelated donor from the donor registry. Bone marrow transplantation allows the cells from the donor’s marrow to take over the Hurler syndrome patient’s own cells, and the donor’s cells can then produce the functional enzyme alpha-L-iduronidase.
In the future, perhaps gene therapy may be used as a treatment for Hurler syndrome. In gene therapy, the gene for alpha-L-iduronidase is inserted into the patient’s own genetic material, and the functioning gene then produces a functional enzyme that replaces the patient’s defective enzyme.